First of all, there are significant differences between playing at private courts versus public facilities. Private Pickleball facilities of course charge a fee which can be per visit, monthly or even annual memberships. Public Courts are normally free but might have a nominal charge for balls, water, etc.

 When Public Courts have no signs then it is just a first come first served situation. This is similar to the way tennis used to be. This also means that any person on any level can play at any time. This is very popular with families especially grandkids and grandparents. These types of players are just there to have fun with their family and are generally not playing in a competitive manner.

On the other hand, many Public Courts do have signs. These signs will usually designate one or more courts as challenge or competitive courts whereas the other courts are more for social play. The better players are on the challenge or competitive court(s) and everyone else is free to play on the social courts.

 This set up seems to work for the largest amount of people with no one feeling "left out". If you have courts under construction in your area (and many do!) it would be advisable to lobby for such signs if they aren’t being planned.

 Sometimes playing schedules are much more detailed. For example, on a Saturday morning they might have 2-3 courts designated for 4.5 level and above. Also, you may see something like Sunday morning team challenge 3.5 level and below.

Designated challenge courts tend to attract 4.5 level and above players. As long as players of a similar level keep coming it will remain a competitive court culture. If the courts get "clogged up" with beginners, over time the better players will stop coming and migrate to a more competitive environment.

 If you are a relative newcomer to Pickleball you are probably wondering by now: “What is this skill level business all about?”  Skill levels range from 1.0 and go in one half point increments all the way to 5.5+. At an informal level you will find out just by playing and asking other players who are usually more than willing to help. Formal definitions have been established the USAPA and are available at: 
https://www.usapa.org/player-skill-rating-definitions/

Your enjoyment of the game will be greatly enhanced as you improve and play others within your skill level. Of course, if you don’t care and just want to get exercise and have fun that’s OK too!